Axial flow gas turbine



July 3, 1962 E. R. M. HOLMQUIST 3,042,366

AXIAL FLOW GAS TURBINE Filed M 4, 1959 2 Sheets-Sheet l IN VENTOR [RNST RUDOLf MAG/VHS HOLMQIHST BY WWW;

ATTORNEY S July 3, 1962 E. R. M. HOLMQUIST 3,042,366

AXIAL FLOW GAS TURBINE 2 Sheets-Sheet 2 Filed May 4, 1959 E RNS' T RUDOIF MAGNl/S HOLMOUIST BY M WM ATTORNEYS 3&4-2366 Patented July 3, 1962 Flee 3,042,366 AXIAL FLQW GAS TURBINE Ernst Rudolf Magnus Holmquist, 16, Lundgrensgatan, Gothenburg, Sweden Filed May 4, 1959, Ser. No. 810,954 Claims priority, application Sweden May 5, 1958 2 Claims. (Ci. 253-3915) The present invention relates to axial flow gas turbines and has for its main object to provide an improved blade wheel for such turbines.

More specifically, the invention relates to turbines having blades of ceramic material. Such blades can withstand very high temperatures but during operation of the turbine they are also subjected to very large mechanical stresses. In turbines of previously known types, these mechanical stresses become detrimental at very high temperatures, which are desired in order to attain the best possible economy of operation. In known turbines of the kind in question the turbine blades are secured to the blade wheel at their inner ends which results in each blade being subjected to a large tensile stress due to the centrifugal force acting on each blade during rotation of the blade wheel. When the blades are simultaneously subjected to very high temperatures they will become elongated so much that they come into contact with the turbine casing and break.

The object of this invention is to provide an improved blade wheel for axial flow gas turbines wherein the blades are not subjected to any considerable amount of tensile stress. This is obtained according to the invention by providing the blade wheel with a ring surrounding the outer ends of the turbine blades in such a way that during operation of the turbine the blades will be caused by the centrifugal force to be pressed against said ring. The blades will then be subjected to compression instead of tension.

Another object of the invention is to provide means for eflicient cooling of the turbine wheel during operation.

A further object of the invention is to provide a turbine structure wherein seizing of the blade wheel or wheels is prevented even at very high temperatures during high speeds of revolution.

The invention will be more fully described herebelow with reference to the accompanying drawings, in which:

H6. 1 is an axial cross section through a blade wheel according to one embodiment of the invention with parts of the stationary casing of the turbine also shown (the bottom of the section being removed for convenience),

FIG. 2 is a segment of the blade wheel seen mainly from the line IIII in FIG. 1,

FIG. 3 is a section to a larger scale through a blade taken on the line IIIIII in FIG. 2 with a portion of the blade broken away, and

FIG. 4 is a section similar to FIG. 3 taken on the line IV--IV in FIG. 2.

Only the details essential for the understanding of the present invention are shown in the drawings. Thus, only one blade wheel is shown together with a portion of the turbine casing, Whereas a gas turbine employing the improvements according to this invention may actually and preferably comprise several blade wheels with stationary guide blades interposed thercbetween in known manner.

In the drawings, numeral 1 designates the turbine shaft which is made hollow for the purpose of passing a cooling fluid therethrough as will be described later. A hub 2 secured to the shaft 1 by means of keys 3 is provided centrally with a circumferential, radially extending flange 4. Two discs 5 of a refractory material, such as Carborundum, are placed around the hub 2 one on each side of the flange 4 and secured to the flange by means of bolts 6 passing through the discs andthe flange and carrying nuts 7. The ceramic discs 5 have larger diameter than the hub flange 4 and, as will be seen from FIG. 1, the outer portions of discs 5 also extend over the rim of flange 4 towards each other. The faces of the outer portions of the discs 5 do not quite meet across the edge of the flange 4 but define between them a narrow slot 8 (see FIG. 4). This slot allows the discs to expand and at the same time assures that the discs are pressed close to the flange 4 by means of the bolts 6 and their nuts 7 which is important in order to obtain ef ficient cooling. 7

The assembly described so far forms the central or nave portion of the blade wheel, This blade wheel central portion carries a number of radially extending pins 9 made of refractotry material, e.g. Carborundum, and arranged like spokes around the periphery of said central wheel portion. The inner ends of the pins 9 are situated in radial bores 10 arranged in the discs 5 at the central slot 8, so that one half of each bore id is situated in one of the discs 5 and the second half in the other disc. Each pin or spoke 9 carries a turbine blade 11 provided with a central bore 12 through which the pin 9 extends. The blades ll are made of an artificial corundum known under the trade name Alundum (A1 0 or a material with similar characteristics. In the outer periphery of the blade wheel central portion formed by the outer portions of the discs 5 there are arranged shallow recesses 13 receiving the inner ends of the blades 11. The rerecesses 13 conform in shape to the cross section of the blades (see FIG. 4) so as to prevent the blades from rotating around the pins 9. There are of course several different ways of constructing the blade Wheel central portion. Thus the slot 3 between the discs may be located towards one side instead of centrally as shown in the drawing, that is one disc 5 may be essentially fiat while the other would be provided with an edge flange extending across the edge of the hub flange 4. The bores 10 and recesses 13 may then be formed in one piece of the discs 5 instead of divided between two pieces as shown.

The blades 11 are surrounded at their outer ends by a ring 14 concentric with the discs 5 and spaced therefrom. The ring 14 is provided in its inner periphery with bores 15 receiving the outer ends of the pins 9 and shallow recesses 16 receiving the outer ends of the turbine blades 11. The ring 1a which is preferably made of the same material as the turbine blades 11, that is Alundum or the like, is surrounded by a metal ring 17 which may be shrunk onto the ceramic ring 14 or secured thereto in any other suitable manner. The metal ring 17 is provided at its outer periphery with a number of circumferential, radially extending cooling flanges 18. The cooling flanges are enclosed between the walls of an annular channel 19 surrounding the ring 17. The channel 19 is formed of sheet metal and secured to the cylindrical casing 26 of the turbine. Numeral Zl. designates an inner cylinder concentric with the casing 20 and having the same outer diameter as the outer diameter of the discs 5 of the blade wheel. The cylinders 24) and 21 are both made of a refractory material and constitute the walls of the annular passage for the hot gas driving the blade wheel or wheels. The channel 19 is provided with an inlet 22 and an outlet 23 (FIG. 2) for a cooling fluid circulating through the channel in order to remove heat from the cooling flanges.

Due to the fact that the blades 11 are not secured to the blade wheel at their inner ends, there will be no elongation of the blades due to centrifugal force when the blade wheel rotates fast. Instead, the blades will be pressed against the ring 14 surrounding their outer ends. The centrifugal force will thus cause a compression of the blades and since the compression strength of the ceramic material in the blades is of the order of ten times the tensile strength, the blades will withstand much higher speeds of revolution combined with higher temperatures than what has been possible with blade wheels of previously known types. As shown in the drawings, the seats in the discs 5 and the ring 14 for the ends of the pins 9 and the blades 11 are made sufliciently deep to allow for expansion of both the pins and the blades under the influence of the high temperatures. It will also be noted that the whole blade wheel is free to expand in radial direction, since the clearance between the cooling flanges 18 on the outer rim of the wheel and the bottom of the channel 19 may be made sufliciently large to allow for any degree of expansion.

As already mentioned, the turbine shaft 1 is made hollow in order to provide passage for a cooling fluid. By using the fuel as cooling fluid a preheating of the fuel is simultaneously obtained. A very efiicient and easily regulated cooling results from carrying away heat both from the center of the blade wheel, via the shaft, and from the outer periphery of the wheel, via the cooling channel 19.

The embodiment hereinbetore described and shown in the accompanying drawings is chosen as an example only and may be modified with respect to its details within the scope of the appended claims. it is also to be understood that the word ceramic is used here in a broad sense and intended to cover all kinds of sintered material containing ceramics, for instance the so called cermets made from a mixture of ceramics and metal powder.

What I claim is:

1. In an axial flow gas turbine, a turbine shaft, a blade Wheel central portion fixedly connected to said shaft, a ring of ceramic material concentrically surrounding but separate from said central wheel portion and being radially spaced therefrom, a plurality of blades of ceramic material extending radially between said blade wheel central portion and said ring, said blade wheel central portion being provided with recesses evenly and angularly spaced therearound and each recess having a configuration corresponding to the cross-section of one of said blades, said blades having their inner ends radially slidable, but non-rotatable in said central portion recesses and being radially unsecured thereby, a steel ring concentrically confining the periphery of and being attached to said ceramic ring, cooling flanges on said steel ring, a

stationary annular channel being provided around said steel ring, said cooling flanges being situated Within said channel and said channel being provided with an inlet and an outlet opening for a cooling fluid.

2. In an axial flow gas turbine, a hollow turbine shaft, a hub fixedly connected to said shaft and having a circumferential flange extending radially from said hub, a pair of discs fixedly connected to said flange one on each side thereof with said discs extending outside of and over said flange and forming the central portion of a blade wheel, a plurality of turbine blades, said blade wheel central portion having a peripheral portion provided with suitably shaped recesses evenly and angularly spaced therearound having the inner ends of said blades radially slidable therein, radially unsecured thereby, and capable of preventing the rotation thereof, a ring of ceramic material concentric with said blade wheel central portion surrounding the outer ends of saidblades, said ring having recesses corresponding to said blade wheel central portion recesses with the outer end portions of said blades loosely positioned therein, a steel ring concentrically confining the periphery of and being attached to said ceramic ring, circumferential flanges extending radially from said steel ring, a stationary annular channel surrounding said steel ring and having said cooling flanges therein, and inlet and outlet connections to said channel for a cooling fluid.

References Cited in the file of this patent UNITED STATES PATENTS 1,362,853 Darling Dec. 21, 1920 2,479,057 Bodger Aug. 16, 1949 2,488,867 Judson Nov. 22, 1949 2,611,248 Ahlen et al. Sept. 23, 1952 2,628,067 Lombard Feb. 10, 1953 2,648,519 Campini Aug. 11, 1953 2,675,672 Schorner Apr. 20, 1954 2,801,789 Moss Aug. 6, 1957 2,838,275 Harris et al June 10, 1958 2,952,442 Warnken Sept. 13, 1960 2,971,745 Warren et a1. Feb. 14, 1961 FOREIGN PATENTS 660,007 Great Britain Oct. 31, 1951 723,505 Great Britain Feb. 9, 1955 

